Typically, railroad tank cars and trucks carry caustic. When tank cars and tanker trucks return to the plant for reloading, the interiors of the vehicles have to be cleaned. Water is used to clean out the vehicles and the water then becomes highly contaminated with metal particles, such as iron and nickel from the reaction process. The present invention relates to a unique environmentally friendly method to clean highly contaminated water containing caustic.
The present invention relates to the manufacture of alkali metal hydroxides, commonly known as caustic. Alkali metal hydroxides are typically from the group which includes sodium, lithium, cesium, potassium and rubidium. Caustic is made using different types of electrolytic cells, including membrane and diaphragm-type cells and then further treating the caustic to concentrate the solution. The present invention is directed to the method of handling water containing sodium hydroxide caustic and metals.
A need has long existed in the caustic industry for a technique to recycle, cheaply, the water used to wash out railroad tank cards and tanker trucks which carry caustic.
Alkali metal hydroxide solutions are typically prepared by the electrolysis of alkali metal salt solutions in electrolytic cells. Diaphragm cells are known for producing alkali metal hydroxide solutions electrolytically. In this type of cell, a porous cathode with an overlying porous diaphragm is used to separate or to serve as a barrier between the catholyte and anolyte compartments of the cell. After separation of the components, the caustic solution is then further treated to increase the concentration of caustic in the solution.
The present invention is directed at a method for reducing the amount of free nickel and nickel oxides, free iron and ferrous oxides in waste water containing alkali metal salts, particularly chlor-alkali salts without the need for additional chemicals.
In order to overcome the disadvantages of the existing systems the present invention proposes the use of magnets in situ in the manufacturing process to overcome these problems with the nickel and the iron for treating waste water containing both caustic and metals.